The present invention concerns a radiation source for producing a planar or flat panel illumination pattern of vacuum ultraviolet (VUV) wavelength radiation that is particularly suited for use in processing of semiconductor wafers up to and beyond 300 millimeters in diameter.
There are a number of uses of short wavelength radiation in the processing of semiconductor wafers for the production of integrated circuits. Short wavelength radiation includes the ultraviolet (UV) ( less than 400 nanometers (nm.)) and vacuum ultraviolet (VUV) (100-200 nm.) regions. This invention addresses a radiation source capable of producing high intensity, uniform UV and VUV wavelength radiation for the processing of semiconductor wafers.
Processing of semiconductor wafers is evolving toward fabrication of smaller features ( less than 0.25 micron) on a wafer. This requires the use of new chemistries, resists, and processes. Many of these new chemistries, materials, and processes require high energy photons to overcome reaction thresholds. Photostabilization of some of the new resists require high energy photons. Ashing and etching of materials and resists in particular can be improved with use of VUV wavelength radiation. High energy photons can excite gases and surfaces in order to enhance reaction processes and reaction rates. Short wavelength radiation is also useful for EPROM erasure, FLASH erasure, and non-volatile memory erasure.
In the present state of the art, there are no acceptable radiation sources for use in the VUV region of wavelengths for treatment of semiconductor wafers. Furthermore, existing radiation sources suffer from one or more of the following shortcomings:
a. Present sources are too low in intensity or have marginal intensity levels, thus, providing inadequate throughput rates.
b. Present sources have large non-uniformity in light output over a two-dimensional area typical of a semiconductor wafer.
c. Present sources are too expensive or complicated to justify use.
d. Present sources have fixed wavelength.
e. Present sources do not provide large enough illuminated area coverage.
f. Present sources produce undesirable wavelengths in addition to desired wavelengths of radiation (e.g., infrared (IR) radiation).
g. present sources can be too large to justify use in a semiconductor fabrication facility due to large xe2x80x9cfootprintxe2x80x9d or floor space required.
h. Present sources require manual loading of wafers.
i. Present sources are too expensive.
j. Present sources utilize bulbs with electrodes, thereby leading to reduced lifetime and degraded output during usable life.
Present technology provides some radiation sources producing radiation having wavelengths below 200 nm. Such radiation sources suffer from unacceptable levels of nonuniformity of the irradiance over the surface of the wafer. This problem usually stems from the use of finite sized lamps such as linear lamps. These lamp configurations are not compatible with a wafer disk requiring uniform illumination over a two dimensional circular area with diameters ranging from 150 millimeters (mm.), or smaller, up to 300 mm., or larger.
The present invention is directed to a tunable UV and VUV wavelength radiation source particularly useful in the treatment of semiconductor wafers. A radiation source constructed in accordance with the invention provides desired wavelengths, intensity and two dimensional planar uniformity of UV and VUV radiation for the treatment of semiconductor wafer workpieces having a diameter of up to 300 mm. or greater. The radiation source of the present invention provides uniformity of illumination intensity across a 300 mm. planar radiation pattern of a few percent or less compared to existing sources on the market which typically claim +/xe2x88x92 15% nonuniformity of illumination intensity.
Advantageously, the radiation source of the present invention is tunable in that it can be operated at a number of distinctly different wavelengths in the region 100-200 nm. or above. In one preferred embodiment, the radiation source output radiation wavelengths can be fine tuned using a gas filter.
The radiation source of the present invention can provide a two dimensional planar radiation source in a selected one of a variety of shapes (e.g., square, circular, etc.). The radiation source is tunable to achieve a desired output radiation wavelength range. Course tuning of the wavelength range emitted by the radiation source is achieved by selecting an ionizable gas that, when energized, produces radiation in a desired wavelength range via excimer excitation of the gas molecules. Additionally, in one preferred embodiment of the present invention, fine tuning of emitted radiation wavelength is achieved though the use of an absorber gas, such as oxygen, which absorbs or filters certain wavelengths of emitted radiation such that a narrower range of wavelengths impinges the target wafer with a modified range of wavelengths. Since different processes are best served by the radiation of different wavelengths, the radiation source of the present invention advantageously provides for flexibility not found in prior art radiation sources.
The present invention is directed to a radiation source for emitting a planar pattern of radiation for use in processing semiconductor wafers. Typically, the emitted radiation will be in the UV or VUV wavelength ranges. The radiation source of the present invention includes: a base electrode having a two dimensional surface bounding a radiation emitting region; a dielectric radiation transmissive member spaced from the base electrode and bounding the radiation emitting region; a two dimensional electrode screen or matrix that is in contact with the dielectric member in a plane generally parallel to the two dimensional surface of the base electrode, the electrode matrix defining a plurality of openings permitting transmission of the emitted radiation through the electrode matrix to a wafer treatment region; a power supply for energizing the base electrode and the electrode matrix; and an ionizable gas disposed in the radiation emitting region for ionization by a field set up between the base electrode and the electrode matrix and emission of radiation via excimer excitation.
In one preferred embodiment of the present invention, the source additionally includes a second protective radiation transmissive member which contacts the electrode matrix and urges the electrode matrix against the dielectric member and functions to protect the electrode matrix from exposure to contaminants in the wafer treatment region and reinforce the dielectric member. Depending on the desired dimension and strength of material characteristics of the dielectric member and the electrode matrix and the pressure differential between the wafer treatment region and the radiation transmission region, the radiation source may additionally include one or more spacer elements inserted in the radiation emitting region between the dielectric member and the base electrode to provide a uniform cross sectional area within the radiation emitting region.
In another preferred embodiment of the radiation source of the present invention, the source gas supply routes a selection of different possible ionizable gases capable of excimer excitation to the radiation emitting region to control a wavelength of radiation emitted by the source. Such selection of a gas from a group of excimer excitation capable gases permits xe2x80x9ccoursexe2x80x9d tuning of the wavelengths generated in the radiation emitting region, i.e., select a gas that generates a desired range of wavelengths when undergoing excimer transitions.
In another preferred embodiment of the radiation source of the present invention, a third radiation transmissive member is disposed in a spaced apart relationship from the second protective member to define a absorber gas filter chamber into which an absorber gas, such as oxygen, is injected. The absorber gas filters or absorbs selected wavelengths of radiation emitted from the radiation emitting region by the ionizable gas. The gas filter provides for fine tuning of the radiation output wavelengths.
These and other objects, advantages and features of the invention will become better understood from a detailed description of an exemplary embodiment of the invention which is described in conjunction with the accompanying drawings.